Don't crash when invalid arguments are provided to the CHANNEL() function

for a SIP channel.
(issue #9619, reported by jtodd, original patch by Corydon76, committed patch
 slightly modified by me)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@62416 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_sip.c

@@ -14911,12 +14911,15 @@ static int acf_channel_read(struct ast_channel *chan, const char *funcname, char
 		return 0;
 	}
 
-	if (strcasecmp(args.param, "rtpqos"))
-		return 0;
+	if (ast_strlen_zero(args.param) || strcasecmp(args.param, "rtpqos"))
+		return -1;
 
 	memset(buf, 0, buflen);
 	memset(&qos, 0, sizeof(qos));
 
+	if (ast_strlen_zero(args.type))
+		return -1;
+
 	if (strcasecmp(args.type, "AUDIO") == 0) {
 		all = ast_rtp_get_quality(p->rtp, &qos);
 	} else if (strcasecmp(args.type, "VIDEO") == 0) {
@@ -14925,6 +14928,9 @@ static int acf_channel_read(struct ast_channel *chan, const char *funcname, char
 		all = ast_rtp_get_quality(p->trtp, &qos);
 	}
 
+	if (ast_strlen_zero(args.field))
+		return -1;
+
 	if (strcasecmp(args.field, "local_ssrc") == 0)
 		snprintf(buf, buflen, "%u", qos.local_ssrc);
 	else if (strcasecmp(args.field, "local_lostpackets") == 0)